attune/work-summary/sessions/2026-01-16-executor-foundation.md

Executor Service Foundation - Session Summary

Date: 2026-01-16 Evening
Phase: Phase 4.1 - Executor Foundation
Status: Core structure complete, needs API refinements

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Overview

Implemented the foundational structure for the Executor Service, the core orchestration engine of Attune. The Executor is responsible for processing enforcements from triggered rules, scheduling executions to workers, managing execution lifecycle, and enforcing policies.

This session focused on Session 1: Foundation as outlined in the implementation plan.

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Accomplishments

1. Executor Crate Structure Created ✅

Created complete directory structure:

crates/executor/
├── Cargo.toml                    # Dependencies configured
└── src/
    ├── main.rs                   # Service entry point
    ├── service.rs                # Main service orchestration
    ├── enforcement_processor.rs  # Enforcement message processing
    ├── scheduler.rs              # Execution scheduling
    └── execution_manager.rs      # Execution lifecycle management

2. ExecutorService Implementation ✅

File: crates/executor/src/service.rs

• Core Features:

  • Database pool integration (PostgreSQL via SQLx)
  • Message queue connection (RabbitMQ via lapin)
  • Publisher and Consumer initialization
  • Graceful shutdown handling with broadcast channel
  • Cloneable service for sharing across async tasks

• Architecture:

  • Uses Arc<ExecutorServiceInner> pattern for thread-safe sharing
  • Spawns multiple processor tasks concurrently
  • Handles SIGINT for graceful shutdown

3. EnforcementProcessor Module ✅

File: crates/executor/src/enforcement_processor.rs

• Purpose: Processes EnforcementCreated messages when rules trigger

• Responsibilities:

  • Listen for enforcement messages from RabbitMQ
  • Fetch enforcement, rule, and event data from database
  • Evaluate rule conditions (skeleton implemented)
  • Create execution records
  • Publish ExecutionRequested messages

• Key Components:

  • EnforcementCreatedPayload struct for message deserialization
  • ExecutionRequestedPayload struct for outbound messages
  • Database repository integration
  • Message envelope handling

4. ExecutionScheduler Module ✅

File: crates/executor/src/scheduler.rs

• Purpose: Routes executions to available workers

• Responsibilities:

  • Listen for ExecutionRequested messages
  • Fetch action metadata to determine runtime requirements
  • Select appropriate worker based on:
    • Runtime compatibility
    • Worker status (active only)
    • Load balancing (placeholder for future enhancement)
  • Update execution status to Scheduled
  • Queue execution to worker-specific queue

• Worker Selection Strategy:

  • Filters by runtime compatibility
  • Filters by worker status (active only)
  • Currently selects first available (TODO: implement load balancing)

5. ExecutionManager Module ✅

File: crates/executor/src/execution_manager.rs

• Purpose: Manages execution lifecycle and status transitions

• Responsibilities:

  • Listen for ExecutionStatusChanged messages
  • Update execution records in database
  • Handle workflow orchestration (parent-child executions)
  • Trigger child executions on parent completion
  • Publish completion notifications

• Status Handling:

  • Supports all execution states: Requested, Scheduling, Scheduled, Running, Completed, Failed, Cancelled, Timeout, Abandoned
  • Special handling for terminal states (Completed, Failed, Cancelled)
  • Workflow triggering on successful completion

6. Service Entry Point ✅

File: crates/executor/src/main.rs

• Features:
  • CLI argument parsing with clap
  • Configurable log level
  • Enhanced logging with thread IDs and line numbers
  • Configuration loading from YAML files
  • Connection string masking for security
  • Graceful shutdown signal handling
  • Comprehensive startup logging

7. Dependencies Configured ✅

File: crates/executor/Cargo.toml

Added dependencies:

• attune-common - Shared models, repositories, message queue
• tokio - Async runtime
• sqlx - Database access
• serde, serde_json - Serialization
• tracing, tracing-subscriber - Logging
• anyhow, thiserror - Error handling
• config - Configuration management
• chrono - Timestamps
• uuid - Message IDs
• clap - CLI parsing
• lapin - RabbitMQ client
• redis - Redis client (for future use)

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Technical Details

Message Flow Architecture

1. Enforcement Created:
   sensor → trigger → event → rule → enforcement
   ↓
   EnforcementProcessor listens on "enforcement.created"
   ↓
   Creates Execution record
   ↓
   Publishes "execution.requested" message

2. Execution Scheduling:
   ExecutionScheduler listens on "execution.requested"
   ↓
   Selects appropriate worker
   ↓
   Updates execution status to Scheduled
   ↓
   Publishes to worker-specific queue

3. Execution Lifecycle:
   ExecutionManager listens on "execution.status.*"
   ↓
   Updates execution state in database
   ↓
   On completion: triggers child executions if needed
   ↓
   Publishes "execution.completed" notification

Message Envelope Pattern

All messages use MessageEnvelope<T> pattern:

• message_id: Unique UUID
• correlation_id: For tracing related messages
• message_type: Enum for routing
• timestamp: Creation time
• headers: Metadata (source, trace_id, retry_count)
• payload: Typed payload struct

Database Integration

Uses repository pattern for all database access:

• EnforcementRepository (from event module)
• EventRepository
• RuleRepository
• ExecutionRepository
• ActionRepository
• RuntimeRepository
• WorkerRepository

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Known Issues & TODOs

Compilation Issues (To be resolved in Session 2)

1. Consumer API Pattern Mismatch:

   • Current code attempts to use consumer.consume() method
   • Actual API uses consumer.consume_with_handler() pattern
   • Need to refactor processors to use handler-based approach

2. Missing Trait Implementations:

   • WorkerRepository needs List trait implementation
   • UpdateExecutionInput needs From<Execution> conversion

3. Unused Imports:

   • Several modules have unused imports to clean up
   • Minor warnings from dead code

Future Enhancements (Later Sessions)

1. Policy Enforcement:

   • Rate limiting logic
   • Concurrency control
   • Queue management for policy violations

2. Workflow Orchestration:

   • Parse workflow definitions from action metadata
   • Extract child actions from execution results
   • Implement DAG-based workflow execution

3. Inquiry Handling:

   • Pause executions waiting for human input
   • Handle inquiry timeouts
   • Resume execution with inquiry response

4. Worker Selection:

   • Implement intelligent load balancing
   • Consider worker affinity (same pack, same runtime)
   • Geographic locality
   • Round-robin or least-connections strategy

5. Error Handling:

   • Retry logic with exponential backoff
   • Dead letter queue for failed messages
   • Circuit breaker pattern for service protection

6. Monitoring:

   • Metrics collection
   • Health checks
   • Performance tracking

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Testing Strategy

Unit Tests (To be implemented)

• Enforcement condition evaluation
• Worker selection logic
• Status transition validation
• Message serialization/deserialization

Integration Tests (To be implemented)

• End-to-end enforcement → execution flow
• Database transaction handling
• Message queue reliability
• Multiple processors running concurrently

Manual Testing (To be implemented)

• Service startup and shutdown
• Configuration loading
• Graceful shutdown handling
• Message processing throughput

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Documentation Updates

Updated Files

• work-summary/TODO.md - Added Session 1 completion, updated priorities
• This session summary document

Technical Documentation (To be created)

• Architecture diagrams for message flow
• Sequence diagrams for enforcement processing
• Worker selection algorithm documentation
• Configuration examples for production deployment

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Metrics

• Files Created: 5 new files
• Lines of Code: ~1,200 lines
• Modules Implemented: 4 core modules
• Dependencies Added: 12 crates
• Compilation Status: Core structure complete, API refinements needed
• Test Coverage: 0% (to be implemented in Session 2)

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Next Steps (Session 2: Enforcement Processing)

Immediate Priorities

1. Fix Consumer API Usage:

   • Refactor all processors to use consume_with_handler pattern
   • Update message handling to be callback-based
   • Test message consumption

2. Implement Missing Traits:

   • Add List implementation to WorkerRepository
   • Add conversion trait for UpdateExecutionInput

3. Clean Up Warnings:

   • Remove unused imports
   • Fix dead code warnings

4. End-to-End Testing:

   • Create test enforcement in database
   • Verify message flow through all processors
   • Validate execution creation and scheduling

Medium-Term Goals

5. Policy Enforcement:

   • Implement rate limiting checks
   • Add concurrency control
   • Queue management

6. Workflow Support:

   • Parse workflow definitions
   • Implement child execution triggering
   • Handle complex execution graphs

7. Production Readiness:

   • Add comprehensive error handling
   • Implement retry logic
   • Add monitoring and metrics

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Lessons Learned

1. Message Queue Patterns: The RabbitMQ library (lapin) uses a handler-based consumption pattern rather than polling. Future code should follow this pattern from the start.

2. Type Safety: Using strongly-typed payload structs with MessageEnvelope<T> provides excellent type safety and makes message handling more reliable.

3. Configuration Complexity: Multiple configuration types (Config vs MessageQueueConfig) can cause confusion. Need clear documentation on which to use where.

4. Repository Pattern: The repository abstraction works well for database access but needs consistent trait implementations across all repositories.

5. Service Architecture: The cloneable service pattern with Arc<ServiceInner> works well for sharing state across async tasks while maintaining thread safety.

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Conclusion

Session 1 successfully established the foundation for the Executor Service. The core structure is in place with proper separation of concerns across three main processors (Enforcement, Scheduling, Management). While compilation issues need to be resolved, the architectural decisions are sound and the codebase is well-positioned for rapid iteration in Session 2.

The Executor is now ready to move from foundation to functional implementation, with the message consumption pattern being the primary blocker to overcome.

Session 1 Status: ✅ COMPLETE (with known issues to address in Session 2)